This invention relates to the art of accelerometers and more particularly to optical fiber accelerometers.
Heretofore, various types of accelerometers have been available. In a first type of accelerometer, a mass was displaced against a spring by the inertial force due to acceleration. The distance which the mass was displaced varied with acceleration. By monitoring the amount of displacement, the acceleration was determined. As the prior art accelerometers were redesigned to measure smaller accelerations, they tended to become more sensitive to interference. The linearity and predictability of the physical change in response to acceleration was a limiting value on the accuracy of accelerometers. When measuring small amounts of acceleration, it was generally difficult to maintain sufficient linearity and predictability.
In one prior art optical fiber accelerometer, a mass was positioned in a housing by transverse diaphragms. The mass was suspended between the ends of longitudinally extending tensioned optical fibers. The tensioned optical fibers were secured to the mass and the housing such that under a component of acceleration along the optic fibers, one fiber was elongated and the other was allowed to contract. A laser transmitted phase coherent light along each optical fiber to a mirrored end thereof and back. The acceleration caused elongation and contraction of the optical fibers, respectively, which altered the phase relationship of the reflected light. The reflected light from the mirrored ends was combined and conveyed to a signal processor or other means for measuring phase shift between the reflected light. The detected phase shift varied in accordance with the acceleration.
The present invention contemplates a new and improved accelerometer which is capable of measuring small acceleration forces accurately over a wide dynamic range.